In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor and ignited for generating hot combustion gasses which flow downstream through several turbine stages. A turbine stage includes stationary turbine vanes extending radially between inner and outer castings. The vanes are hollow with openings that mate to openings within the castings. The vanes have airfoil configurations for guiding the combustion gasses between corresponding turbine rotor blades disposed downstream of the vanes. The blades are mounted to the perimeter of a rotor disk that rotates during operation for providing power to turn the compressor or fan during operation. Since the turbine vanes are heated during operation by the hot combustion gasses which flow thereover, cooling air bled from the compressor is channeled inside the vanes for cooling thereof.
In order to increase the efficiency and the performance of gas turbine engines so as to provide increased thrust-to-weight ratios, lower emissions and improved specific fuel consumption, engine turbines are tasked to operate at higher temperatures. As the higher temperatures reach and surpass the limits of the material comprising the components in the hot section of the engine and in particular the turbine section of the engine, new materials must be developed.
As the engine operating temperatures have increased, new methods of cooling the high temperature alloys comprising the combustors and the turbine airfoils have been developed. For example, ceramic thermal barrier coatings (TBCs) have been applied to the surfaces of components in the stream of the hot effluent gases of combustion to reduce the heat transfer rate and to provide thermal protection to the underlying metal and allow the component to withstand higher temperatures. These improvements helped to reduce the peak temperatures and thermal gradients. Simultaneously, ceramic matrix composites were developed as substitutes for the high temperature alloys. The ceramic matrix composites (CMCs) in many cases provided an improved temperature and density advantage over the metals, making them the material of choice when higher operating temperatures were desired.
A number of techniques have been used to manufacture turbine engine components. One such technique includes manufacturing turbine blades from CMCs. One method of manufacturing CMC components, set forth in U.S. Pat. Nos. 5,015,540; 5,330,854; and 5,336,350; incorporated herein by reference in their entirety and assigned to the assignee of the present invention, relates to the production of silicon carbide matrix composites containing fibrous material that is infiltrated with molten silicon, herein referred to as the Silcomp process. The fibers generally have diameters of about 140 micrometers or greater, which prevent intricate, complex shapes, such as turbine blade components, from being manufactured by the Silcomp process.
Another technique of manufacturing CMC turbine blades is the method known as the slurry cast melt infiltration (MI) process. A technical description of such a slurry cast MI method is described in detail in U.S. Pat. No. 6,280,550 B1, which is assigned to the Assignee of the present invention and which is incorporated herein by reference. In one method of manufacturing using the slurry cast MI method, CMCs are produced by initially providing plies of balanced two-dimensional (2D) woven cloth comprising silicon carbide (SiC)-containing fibers, having two weave directions at substantially 90° angles to each other, with substantially the same number of fibers running in both directions of the weave. The use of two dimensional plies prevents intricate, complex shapes, such as turbine blade components, from being manufactured.
One disadvantage of existing methods for production of CMC preforms is that the fibers that provide advantageous structural properties to a composite are not positioned and interlocked or interwoven to provide an optimal fiber architecture. Conventional methods of three-dimensional composite performing typically involve fabricating woven, or braided shapes that do not provide the desired complex preform shapes. What is needed is a method of weaving a three-dimensional composite preform that provides a tailored fiber architecture which may be assembled “near-net-shape”.